[time-nuts] GPSDO module connections

GandalfG8 at aol.com GandalfG8 at aol.com
Mon Mar 3 15:53:19 EST 2014

It might also be worth noting that whilst manufacturers such as  Trimble do 
recommend the use of RG59 or similar 75 ohm cable for GPS module  antenna 
connections this is based on its lower loss compared  with 50 ohm equivalents 
such as RG58.
The connector itself on the GPS module, in most cases if not all, will  
still be a 50 ohm connector but it's considered that the lower cable  
attenuation will more than compensate for any mismatch effects.
In overall cable loss terms it isn't going to make any difference whether  
75 ohm RG59 pigtails are used for the internal connections or whether 50 ohm 
 RG58 is used instead, it will just shift the position of the mismatch 
we're  planning to ignore anyway:-)
However, RG58 does tend to be better quality, particularly when it comes to 
 the braided screen, some RG59 has a very open weave indeed, and this does  
generally make the RG58 easier to work with and might also ensure a more  
reliable connection.
If it were me I would maintain the 50 ohms impedance within the unit and  
then switch to 75 ohms externally, assuming of course that's what I chose to 
do  rather than stay with 50 ohms right through.
In a message dated 03/03/2014 19:42:38 GMT Standard Time,  
n1hac at dartmouth.edu writes:

RG-59  cable is fine but soldering wires is not a good idea for 1.6GHz.  
Use  a panel-mount BNC crimp connector made for RG-59 such as the 
Amphenol  31-343-RFX.  I presume you want to use regular 50 ohm BNC types  
rather than the 75 ohm variant.

It is preferred to use coax for the  1 PPS as any reflections will 
degrade its risetime.

Good  luck,


On 3/3/14 1:01 PM, d0ct0r wrote:
>  Hello,
> I am looking for the advise: what will be the better  method to connect 
> GPSDO module by short extension cable to put its  antenna input on 
> front or back panel ?
> Lets say,  GPSDO module has female “F” connector. And I would like to 
> have BNC  connector on back panel of my project. Manufacturer of GPSDO 
>  recommend to use RG-59 cable for antenna connection.
> Is it OK if I'll  take some RG-59 from CCTV, cut 6" or 12" of it, 
> connect one end to  GPSDO (let say this cable has compression type 
> connector) and solder  other end to BNC on the panel ? Or its better to 
> use adapters and no  soldering ? Like "F connector-to-BNC" adapter , 
> then short BNC-to-BNC  cable connected to BNC panel connector ?
> And other question:  is it worth to use RF cable to connect 1PPS output 
> from GPSDO to  distribution amplifier ? Or regular AWG-22 could do that 
> job ? Thanks  !

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